Treatment of magnetic materials



W. FONDILLER TREATMENT OF MAGNETIC MATERIALS Filed 59101;. 5, 1920 AMFEHES 0 0.4 0.5 L0 L5 v 20 AMPERES MY/fiam Fond/Wen Patented Aug. 7, iii 23.

WILLIAM EONDILLER, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY, moonrona'rnn, or NEW roan.

YORK, N. Y., A CORPORATION OF NEW TREATMENT OF MAG1\TETIC MATERIALS.

Application filed September T all whom it may concern Be it known that I, William FONDILLER, a citizen of the United States of America, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in the Treatment of Magnetic Materials, of which the following is a full, clear, concise, and exact description.

This invention relates to an electrical treatment of magnetic materials.

One of the important characteristics of magnetic material when it is to be used in conjunction with electrical apparatus and electrical circuits, is its permeability to the magnetizin forces produced by electrical currents. he term permeability, u, is ordinarily defined as being the ratio of the magnetic induction, B, induced therein by a magnetizing force, H, to the magnetizing force; i. e.

This truly defines the magnetic state of the material only when, previous to its subjectio to the magnetizing force, it is an entirely neutral magnetic state. If, however, the material has been subjected previously to other magnetizing forces, it is necessary to take into account the residual magnetism which remains therein. The usual method employed to determine the permeability of a magnetic material is to completely demagnetize it prior to the permeability measurement in order to remove the effects of any previous magnetic history.

The superposition of a direct current upon a weak alternating current also causes considerable alteration in the magnetic properties of the material, which phenomena have heretofore been little understood. Thus, it has been erroneously assumed that the permeability of a magnetic material to a weak alternating current may be increased by causing the magnetizing force produced by a rather large direct current to act simultaneously thereon. That such an effect is not produced will be apparent from the consideration described of the results of the investigation hereinafter which form the bases of the. present invention.

In constructing certain apparatus for use in electrical circuits, it has often been desired to obtain a precise value of permeabil- 3, 1920. Serial No. 408,113. 1

ity in the magnetic material, which is used in such apparatus at a definite weak magnetizing force. This has been accomplished in the past by subjecting the material to mechanical and heat treatment whereby the magnetic properties of the material are altered. In a great many cases, however, such a method is not feasible, while in others it does not produce sufficiently accurate re sults, but up to the present time no other method has been available.

It is the object of this invention to provide a method whereby the permeability to signaling currents ofmagnetic material may be altered to a desired value by electrical treatment.

In the drawings, Fig. 1 shows the relation between the magnetizing force and the magnetic induction produced in a magnetic material by a signaling current and a direct current superposed thereon; Fig. 2 shows the relation between the percentage reduction of permeability and the constant magnetizing force required to produce such reduction; Fig. 3 shows the relation between the percentage reduction of permeability and the initial amplitude of the demagnetizing current required to produce such reduction, and Fig. 4 shows a diagram of a typical circuit arrangement which is used in carrying out .this invention.

For the small range of change of magnetization produced by weak currents such as signaling currents the permeability is sensibly constant and the hysteresis loss extremely small. Such a cycle of magnetization may therefore be re resented by a very narrow loop and the e ective permeability in the cycle may for all practical purposes be taken as the slope of the straight line connecting the tips of the loop. Thus, assuming that the signaling current alone is flowing in the circuit, the small loop representing the cycle of magnetization is shown at l in Fig. 1 of the drawings. The line drawn through the tips of the loop, whose slope, as has been pointed out above, may be taken to represent the effective permeability in the cycle, is shown to be at an angle a with the horizontal. llf now, a direct current of sufficient amplitude to give amagnetizing force H be superposed upon the signaling current, the loop 2 will represent the cycle of magnetization, it making an angle (iwith the horizontal, 6 being less than a. If now the direct current be removed, the magnetic induction in the material due to the direct current will decrease until the corresponding residual value is reached, and this may be shown graphically by line 2-3-4. The loop 4 due to the signaling current when this condition is reached is at an angle {5 with the horizontal. It will be apparent that (5 is less than a but greater than (i. If new a direct current suiiicient to give a magnetizing force H be superposed upon the signaling current, the magnetic induction in the material due to the direct current will increase along the path 45 2-6. The si naling current loop 6 makes an angle 9 wit the horizontal at this point. Assuming that the direct current be removed, the magnetic induction in the material due to the direct current is reduced to a new residual value, as shown by the path 67- 8. The signaling current loop at this point is designated by 8, and it makes an angle 6 with the horizontal. It may readily be shown by experimentation, that substantially the same loop is obtained whether a direct current suiiicient to produce a magnetizing force H, is superposed upon the signaling current, and kept there, or whether a direct current sufficient to produce a magnetizing force H is superposed upon the signaling current and then removed.

The manner in which this invention employs .the phenomena described herein will now be explained. It is often desired to produce a certain permeability to signalin currents in a piece of magnetic material. eretofore it has been considered necessary to subject the magnetic material to a mechanical or heat treatment, or both in order to effeet the desired change, which method could not be applied to a manufactured article whose configuration would be altered or destroyed by such treatment. It will be shown herein, however, that the permeability of a magnetic material to signaling currents may be controlled over a considerable range by means of an electrical treatment.

The preferred method of treating magnetic material electrically to obtain a certain value of permeability to signaling currents will be hereinafter described.

By reference to F ig. 3, whose ordinates represent percentage permeability to signaling currents, and whose abscissm represent amperes of a demagnetizing current-either by reversals of direct current or by an alternating current-the initial amplitude of such demagnetizing current to give the desired decrease in permeability may be determined. As in the case above, it will be assumed that a permeability of seventy per cent of the original value to signaling conductorsis desired. The material is first sub-- jected to the influence of a direct current of sufiicient amplitude to magnetize the material to its saturation point. When this current is removed the saturation value of residual magnetism is produced in the material. Then an alternating current having an initial amplitude of 0.15 amperes, which value is derived from Fig. 3, is applied, and by degrees the current is gradually reduced to zero. VVhen'this point has been reached it will be found that the permeability of the material to signaling currents is seventy per cent of its original value.

While the present invention is adapted to be applied in a great variety of ways, its use in connection with the loaded conductors of a submarine cable will be hereinafter more specifically referred to. It has been found that, in utilizing two pairs of loaded conductors as component parts of a phantom circuit employing amplifiers, the permeability of the loading material to signaling currents must be substantially uniform throughout the entire circuit. That is, each separate length ing in a substantially uniform magnetic state, and the loading of each conductor as a whole must be at a balance with the loading of the other three conductors. By subjecting each conductor to the treatment de scribed hereinabove, such a uniformity may be realized. In Figure 4:, the four loaded conductors 9, 10, 11 and 12, form the component parts of a phantom circuit. Assume that the loading of conductors 10, 11 and 12 is in a uniform magnetic condition, and it is required to so treat the loading of conductor 9 that it will make possible a balanced system. Preliminary measurement of the permeability of the loading material of conductor 9 shows, for example, thatit must be reduced to seventy percent of its original value in order to effect the desired result. The conductor 9 at one end is connected to ground 13 and at the other end to one terminal of a two-way double pole switch 14. The other terminal of the switch is connected through the variable resistance 15, and ammeter 16, to ground 17'. A voltmeter 18 is placed in shunt with the switch 14. The direct current source is represented by 19, a direct current generator, and the alternating current source by 20, an alternating current generator. The switch is first thrown so that the direct current generator is in circuit, and the resistance at 15 so adjusted as to give a strength of current sufficient to produce the saturation value of residual, magnetisrn in the loading of the conductor 9. The switch is then reversed, so that the al ternating current generator is in the circuit, andthe resistance at 15 so adjusted that the required initial amplitude of the alternating current may be that indicated in accordance with Figure 3. The current is then gradually diminished, until the zero point is reached. The loading of conductor 9 will of each conductor must have its loadmeager then have the desired permeability to signaling currents, and uniformity will have been attained throughout the phantom circuit.

It will be apparent that the chan e which has thus been produced terial is stable only as long as the signaling currents themselves are small in com arisen with the currents used in adjusting t e state of the material. F or all practical pur oses, however, for-currents which will pro uce a magnetizing force, up to say, H=0.2., the magnetic condition as produced in accordance with the process as set forth above, will be stable.

What is claimed is Y 1. The methodof adjusting the permea: bility of magnetic materials to sialing currents to a desired degree, which consists in the loa mg ma in producing in said magnetic material'the saturationvalue of residual magnetism and then subjecting said magnetic material to a cyclic demagnetization utilizing a current of predetermined amplitude.

2. The method of balancing continuously loaded signaling conductors, which consists in producing in the loading material of certain of the conductors the saturation value of residual magnetism, subjecting said loading material to a demagnetizmg current of a predetermined amplitude, and then[reducing the amplitude of said pulsating current to zero. Y

In witness whereof, I hereunto subscribe my name this 27th day of August A. 11)., 1920..

WILLIAM FUNDJILLER. 

